Naturally they'll need a food source, so assuming you have a healthy population of insects for them to prey upon that should take care of that department.
Shelter is needed for a frog/toad habitat. They instinctively prefer to remain hidden whenever possible to keep from getting eaten by snakes, birds and other predators. They'll hide under lush foliage, rocks, logs and anything that can hide them from their enemies. There are even Toad Houses designed to attract them. Toad houses serve a function of helping to keep toads on your property while providing ornamentation pleasing to the human eye.
Moisture - Water. Frogs will not be found if there is no body of water nearby, toads however can be found miles from the nearest body of water but being amphibians they still need moisture. They don't drink through their mouth, they absorb moisture through their skin by sitting in water. An outdoor pond or even bird baths set low to the ground will help. The water serves a dual function, it attracts mosquitoes, which breed in water. The mosquitoes provide a food source for your amphibian friends and the pond / water provides moisture. This of course could back fire on you if you fail to attract toads and the mosquito larvae hatch.
Stocking your Own Frogs and Toads
In addition to attracting toads and frogs you can also stock your own. The easiest way is to go out and get them, well okay maybe not all that easy - those suckers are fast, any kid not wasting away on the video game circuit can tell you that.
The nearest forest, pond, lake is bound to harbor frogs, toads and pollywogs indigenous to your region. Once you catch them you'll want to have a habitat set for them in which they'll choose to dwell and stay near.
They can also be purchased online but you'll want to be certain you get a species indigenous to your area in order to ensure survival. Online retailers will sell you a habitat with a coupon to have live amphibians shipped to you.